Traps, such as bottle traps or convoluted pipes, are widely used throughout the world to connect waste fluid outlets from sinks, baths or showers or the like to a soil stack. A conventional trap comprises an inlet and an outlet, and defines a passageway for liquid to flow from the inlet to the outlet. A conventional trap is designed such that, in use, liquid is retained in the passageway to provide a barrier between the inlet and the outlet, preventing odours and gases from the soil stack passing through the trap into the surrounding environment.
Whilst conventional traps are fairly effective, there are drawbacks associated with them. It is known, for example, for the liquid seal to evaporate over a period of time, such that the gases in the soil stack are no longer prevented from escaping through the waste outlet. This is particularly a problem where the waste outlet is not used regularly and/or the trap is located in a hot or low humidity environment in which the rate of evaporation is increased.
It is also known for a siphon effect to be established in a trap causing the liquid in the trap to be sucked out of the trap, thereby breaking the liquid seal.
Non-return devices have been used in conjunction with soil traps to prevent odours from the soil stack passing through the trap in the event of the liquid seal being broken. One such device is described in GB2296309. However this device has drawbacks. For example the incorporation of such a non-return device may restrict the flow through the waste outlet and causing a build up of fluid in the vessel. This can be unsightly and prompt concern of a blockage in a user.
It is also known for conventional non-return devices to turn inside out when there is a pressure differential across the device resulting in a higher pressure on soil stack side of the non-return device, thereby negating the effect of the non-return device.